phabricator: verify local tags before trusting them Previously we trust local tags blindly and that could cause wrong Differential Revision to be updated, when people switch between Phabricator instances. This patch adds verification logic to detect such issue and remove problematic tags. For example, a tag "D19" was on node "X", the code will fetch all diffs attached to D19, and check if nodes server-side overlaps with nodes in precursors. If they do not overlap, create a new Differential Revision. Test Plan: Use a test Phabricator instance, send patches using `hg phabsend`, then change the local tag manually to a wrong Differential Revision number. Amend the patch and send again. Make sure the tag gets ignored and deleted. Differential Revision: https://phab.mercurial-scm.org/D36